Conventionally, a method for fixing a fluid device unit to an installation surface is known, in which a through-hole is bored in a base part provided at a bottom of the fluid device unit, and a fastening bolt is inserted from above the through-hole (e.g., see PTL 1). When seen in plan view from above the fluid device unit, the fluid device unit with the through-hole bored in the base part assumes a shape in which the base part, where the through-hole is bored, protrudes from a main body part of the fluid device unit.
Another known method involves boring a fastening hole in a bottom surface of the fluid device unit and inserting a fastening bolt from below the installation surface, where a through-hole is bored, to fasten the bolt to the fastening hole.